The present invention relates generally to clutches, and more particularly to viscous clutches.
Viscous clutches are used in a wide variety of applications, such as for automotive fan drive applications. These clutches typically employ relatively thick silicone oil (more generally called shear fluid or viscous fluid) for the selective transmission of torque between two rotatable components. Engage or disengagement the clutch is made possible by selectively allowing the oil into and out of a working area of the clutch located between input and output members (e.g., between a rotor and a housing) where a viscous shear coupling can be created by the oil to transmit torque from the input member to the output member. A valve is used to control the flow of the oil into and/or out of the working area. Some recent clutch designs allow the oil to be stored in a reservoir attached to an input rotor (located inside the housing and generally accepting a torque input at all times) while the clutch is disengaged, in order to keep kinetic energy available in the oil to allow rapid engagement of an outer output housing of the clutch from the disengaged/off condition, and to allow the clutch to have a very low output speed (e.g., fan speed) while the valve is positioned to obstruct oil flow into the working area. However, attachment of the reservoir to the rotor disk substantially limits design flexibility. For instance, many prior art viscous clutches have limitations associated with magnetic flux circuits used for control of the valve, and positioning a valve relative to a rotating reservoir while still providing suitable fluid and flux paths presents formidable challenges. These constraints typically apply while designers also still seek to provide a relatively compact and low-mass clutch package that can accommodate desired torque loads and also function quickly, efficiently and reliably.
Therefore, it is desired to provide an alternative viscous clutch.